2024 Cedar S4 Physics Prelim Solutions

Physics Prelim 2024 P1&2 answers 1 2 3 4 5 6 7 8 9 10 B A D B D A D C C C 11 12 13 14 15 16 17 18 19 20 A C A D A D B D A A 21 22 23 24 25 26 27 28 29 30 D A A C C D C A A D 31 32 33 34 35 36 37 38 39 40 A C C C A A D D D C 1a(i) 0.0 m/s 1 1a(ii) 5.0 m/s. 1 1b She is correct, since acceleration is the rate of change of velocity/acceleration exist when velocity changes [1] and the direction of the velocity is continously changing[1], and there is acceleration throughout the motion. OR There is a change of direction of movement, thus there is a net force acting on water in wheel. [1] Since resultant force = ma, there is an acceleration. [1] 2 2a(i) Taking moments about the balance point, Since its in equilibrium, Sum of anticlockwise moments = Sum of clockwise moments F1 (d1) = F2 (d2) (550)(0.86) = W(1.1) W = 430 N 1 1 2a(ii) The see-saw rotates anticlockwise/ girl move down while boy moves up. The anti-clockwise moment increases more than the clockwise moment (at any time)./ The total anticlockwise moment is higher than the total clockwise moment. 1 1 2b 1. When displaced, there is a perpendicular distance between the line of action of weight and the pivot. OR line of action of weight falls on the right of pivot. 2. The weight of the toy thus provides a clockwise moment about the pivot . Cannot discuss anticlockwise because not in existence. 3. The toy returns to the original position eventually where the line of action of the weight passes through the pivot OR c.g. is vertically(directly) below pivot. (Either statement 1 + 2 or statement 2+ 3) O level will require all 3. 2 3a Ptrapped gas= 10 cm Hg + Patm = 86 cm Hg Ptrapped gas = (86/1 000) x 13600 x 10 = 1.17 x 105 Pa 1 1 3b Equal height drawing at 55 cm 1 4ai Refraction 1 4aii The wavelength becomes smaller[1] suggesting that the speed of the wave decreases[1] OR The angle of incidence is larger than the angle of refraction/ wave bends towards the normal[1], therefore the speed of the wave slows down.[1] 1 1

Physics Prelim 2024 P1&2 answers 4bi f=0.39/(0.026*2) =7.5 Hz 1 1 bii Refractive index = sin(45)/sin(33)=0.39/v allow ecf if error is penalized in bi v = 0.30 m/s OR Sin 45 = 0.052 / H Sin 33 = new wavelength / H New wavelength = (0.052 x sin 33) / sin 45 = 0.040 m v = wavelength x frequency = 0.04 x 7.5 = 0.300 m/s 2 1 1 1 5ai I=P/V=0.90 W/6.0 V =0.15 A I=0.15 + 0.1 = 0.25 A 1 1 5aii Charge = 0.25*1.5*60*60 allow ecf from ai =1350 C 1 1 5b Resistance of the LDR decreases as light from the lamp falls on LDR. Current across the branch increase with LDR. Therefore power dissipated by the lamp increases, brightness increases. 1 1 5ci 1 cii fire leads to hot and bright conditions, therefore resistance of the LDR decreases and resistance of thermistor decreases. low potential difference across the LDR and thermistor High pote